DIGI-EGOR ideas

[John Dammeyer]

Hi all,

I'd rather see the subject name be DWBO2 for DIGI Wide Band O2 so that Good
ol what's his name doesn't get upset about using EGOR which he's probably
got trademarked by now.

>
> Date: Thu, 23 Nov 2000 20:56:24 +1100
> From: Peter Gargano <peter at techedge.com.au>
> Subject: DIGI-EGOR ideas
>
> Re: DIY-GOR (sic) ideas (was: No Subject)
>
> Bruce Plecan wrote:
> >
> > How about changing the subject line?.
>
> Done!
>
> > You also destroying the intent of using the DIY-EGOR diagrams.
>
> I think DIGI-EGOR (if I can be so bold as to suggest the name) is not
> the same as the project at http://diy-efi.org/diy_efi/projects/diy_egor/
>
> > why this reinventing of the wheel escapes me.

I don't think it's re-inventing the wheel.  The analogue circuit is far more
complex than the digital one will be and much harder to tweak.

Some comments on the digital one.  Watch out for discreet H-Bridge circuits
especially with FETs.  The Gate capacitance can cause the device to slowly
shut off and have the two devices ON at the same time.  Much better here to
use a Motor Driver type H-Bridge.  One device that comes to mind is the
L293E  (not D) which brings the current sensing legs to the outside of the
package.  I'll check the data sheets to see if it would work well in the 5ma
range since it's a 1 AMP device in a 20 pin DIP package.  The 2993 from
Allegro may also work and is also in a 20 pin DIP package.  The Veb at CE
saturation is about 1.2V at 1A.  The spec sheet doesn't say what it would be
at 5ma.

Filtering the PWM signals for Steppers is usually something like a 10K
Resistor and a 0.1 uFd capacitor but it could be as low as 0.001 depending
on the response time desired.  i.e. The conversion speed of the A/D is fast
enough that as long as the RC network kept the signal from changing during
the conversion time there won't be a problem.

Since the heater is resistive device inductance and rise time doesn't figure
into it so it's pretty easy to turn on the transistor and include the
measure current routine in a tight loop or interrupt routine so that as soon
as the current increases past a set point the transistor gets turned off.
Keeping those set points in the EEROM and being able to modify them from
Hyperterm on the PC allows huge flexibility.  It might be worthwhile to add
an external comparator to gate the Heater Drive off if the current exceeds
some threshold.

I'll check today to see if the Honda dealer here has a WBO2 in stock.  I
really don't have any time to do this circuit right now but it's just really
interesting...and I have most of the bits and pieces and I have a set of
Gerbers ready to go to a PCB manufacturer so adding one extra little
board....

sigh...  so much to do ... never enough time....


John Dammeyer.



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